1. Field of the Invention
The present invention relates to a clock regeneration circuit, and in particular to a bit free clock regeneration circuit which enables a clock extraction not depending on a bit frequency, and an optical signal receiver using the same.
2. Description of the Related Arts
In a transmitter, a clock of a reception signal is extracted as a self-synchronous type, and a reception timing of the reception signal is determined in synchronism therewith. For this reason, a clock regeneration circuit for extracting the clock from the reception signal is necessary.
Until now, in a transmission system, generally speaking, a bit rate of the clock in the reception signal is already known, and the clock regeneration circuit at a receiver side was structured corresponding to this fact. A SAW filter is used, or a PLL system is used, and a circuit for extracting and regenerating the clocks of a devotedly signal frequency is used as a clock regeneration circuit.
On the other hand, in recent years, an optical transmission system is spread, and the transmission of a large capacity is further possible due to an optical multiplexing.
FIG. 1 is an example of an optical transmission system, and in a configuration of a transmission side device 20, a multiplexer 200 multiplexes a signal, and an optical transmitter 201 converts it into an optical signal of a single wavelength to transmit it to a reception side device 21 via an optical fiber transmission path 22.
In the reception side device 21, a light receiving element 210 converts the received lights into an electric signal, and a pre-amplifier 211 and a main amplifier 212 amplify it to a predetermined level. Furthermore, the amplified reception signal are sent to a discriminator 214 and a clock regeneration circuit 213.
The clock regeneration circuit 213 extracts a clock signal synchronized with a frequency of the reception signal. At a timing of a clock signal extracted, the discriminator 214 discriminates and outputs the reception signal as data. Furthermore, the clock signal is sent to a multiplexing separation circuit 215 to separate the multiplexing of the reception signal discriminated and output from the discriminator 214.
Here, the optical transmission system in FIG. 1 uses an optical transmission signal of clock frequencies of 155 Mb/s, 622 Mb/s, or 2.4 Gb/s in response to the transmission capacity. Accordingly, it is necessary that the clock regeneration circuit 213 of the optical reception side device 21 prepares the clock regeneration circuits 213 differing respectively corresponding to the clock frequencies for use in the transmission system.
Furthermore, in recent years, in an optical communication, development and practical use of a wavelength division multiplexing communication system are being advanced. The wavelength division multiplexing communication system transmits an optical signal of a large capacity in which frequencies are divided and multiplexed by a WDM (Wavelength Division Multiplexing) system. FIG. 2 is a configurational example of such the wavelength division multiplexing system. An existent system 30 as a transmission side device is a signal source for generating and outputting a plurality of optical signals.
A separate optical signal from the existent system 30 is received, and an optical/electric signal converter 31 converts it into a corresponding electric signal. The optical/electric signal converter 31 converts into an electric signal, and after a predetermined signal processing is effected, an electric/optical signal converter 32 again converts it into an optical signal.
The plurality of optical signals from the electric/optical signal converter 32 are converted into an optical signal of a wavelength corresponding to each signal by an optical multiplexer 33, which transmits it to an optical transmission path 34 as a wavelength division multiplexing signal.
A wavelength division multiple optical signal propagates through the optical transmission path 34, and is input to an optical multiplexing separator 35 of the reception side device. The wavelength division multiplexing optical signal is separated to a separate optical signal in each wavelength, and is converted into an electric signal by a corresponding optical/electric signal converter 36.
As occasion demands, an electric/optical signal converter 37 again converts into an optical signal, and an existent system 38 converts it into an electric signal, and a separate optical signal is processed in each wavelength.
Accordingly, in a system example of FIG. 2, in the existent system, the clock regeneration circuit corresponding to each wavelength is necessary.